1. Field of the Invention
The present invention relates to a printed circuit board having a semiconductor device mounted on a printed wiring board.
2. Description of the Related Art
In recent years, along with an increase in consumption current of a large-scale integration (hereinafter referred to as “LSI”) as a semiconductor device, a malfunction of the LSI caused by fluctuations in power potential and ground potential has been a problem.
Operation of an LSI generates a potential fluctuation (power noise) that is determined by the product of a current flowing through a power terminal and a ground terminal and an impedance of the LSI as seen from the power terminal and the ground terminal. When the potential fluctuation propagates through a power pattern and a ground pattern of the printed wiring board, a power potential and a ground potential for operating another LSI may fluctuate to cause a malfunction of the LSI.
One conceivable method for suppressing the propagation of the fluctuations in power potential and ground potential caused by the operation of the LSI is decoupling, which electrically separates the power terminal of the LSI from the power pattern of the printed wiring board in a high frequency region. Therefore, an inductance element is conventionally interposed between the power terminal of the LSI and the power pattern of the printed wiring board. However, the number of components increases because the inductance element is interposed.
To deal with this problem, it has been proposed to decouple LSIs by forming an elongated meander power pattern in the printed wiring board so as to increase an inductance value of the power pattern (see Japanese Patent Application Laid-Open No. 2001-119110).
However, although the inductance value of the power pattern can be increased as the power pattern becomes thinner, an electric resistance value of the power pattern is also increased at the same time. The increased electric resistance value of the power pattern results in a large power voltage drop that is determined by the product of a DC current supplied to the LSI (average consumption current) and the electric resistance value of the power pattern. Thus, a DC power voltage for driving the LSI may become insufficient.